This invention relates to corpuscular energy beam produced microasperities for lubrication. More particularly, this invention relates to an apparatus such as a laser apparatus or other producing a beam of corpuscular energy for producing controlled microasperities on surfaces such as bearing surfaces.
In rotating machinery, and especially where rotating shafts operate partly within a housing that contains fluid under pressure, dynamic seals are used. These dynamic seals consist of two basic parts, a rotor and a stator. The stator is fixed to the housing, whereas the rotor bears against the stator and is fixed to a shaft passing through the housing. In high pressure and temperature applications, and especially where leakage must be kept to a minimum the metal rotor rotates against a wear resistant stator of carbon material. Of course, with the rotor heavily loaded against the stator to ensure good sealing, wear is enhanced. This results in frequent replacement of the seals, resulting in unwanted down time and cost.
Somewhat by accident it was found that thin films were forming between the rotating surfaces of face seals in certain applications. These films apparently existed in spite of the high loading forces placed on the seals. It was also found that the presence of these thin films of lubricant on the seal during operation resulted in considerably longer seal life. This led to research into thin film lubrication mechanisms and the use of microasperities to produce such films of a controlled thickness.
Microasperities are small projections or protuberances intentionally formed on one or both of the bearing surfaces of a seal. These small protrusions or bumps have been found to produce the desired thin film of lubricant and retain it during dynamic operation of the seal. With this lubrication system, cavitation of the lubricant film occurs at the trailing edge of the microasperities and flow of lubricant around and over the microasperities produces a pressure distribution that supports the load by controlled oil film thickness, producing a separation of rotor and stator. The separation produced by the controlled oil film in the field of microasperities is much greater than with a smooth lapped surface. This has the effect of reducing the localized and surface gouging by small carbides, and therefore greatly reduces wear. The variables involved are the size and shape of microasperities, the viscosity of the lubricant liquid, the rotor velocity and the thickness of the liquid film over the microasperities.
Microasperities have been formed in numerous ways, and predominantly by chemical milling of photoetched, previously finished surfaces. Additional techniques include lapping, coining, and other etching techniques.
These techniques have been somewhat refined to the point where there has been a progression from randomly sized and shaped asperities to attempts to produce homogeneous asperity surfaces. The homogeneous surfaces are of course more amenable to analytical prediction. Cylindrical asperities in a geometric array have been produced by using photoetching techniques. These asperities have a circular contact surface. More recently, triangular shapes have been considered. See, for example: Dennis Lee Otto, Triangular Asperities Control Seal Leakage and Lubrication, Society of Automotive Engineers, Paper No. 740201, 1974.
However, these triangular asperities, as with the aforementioned circular asperities, have flat plane contact surfaces which are the necessary result of using chemical etching techniques wherein the unetched surface is merely masked by use of a coating. Other more complex shapes, such as pyramidal or ramp shaped, have been proposed, which would require new manufacturing techniques.
The present invention utilizes a means for producing a beam of corpuscular energy and a control means therefor, such as a beam chopper, for producing microasperities of a controlled size, shape and density on bearing surfaces. The beam of corpuscular energy is conveniently a laser beam, an electron beam, or a spark discharge. As an alternative to a mechanical beam chopper, the duration of the beam may be controlled by electronically pulsing the beam. The shape of the microasperity produced is pyramidal, or ramp shaped. An abrupt frontal wall and a tapering rear wall of such shaped asperity produces a desired cavitation effect and consequently enhanced seal dynamics.